5 research outputs found
The Hyperactive L Dwarf 2MASS J13153094-2649513: Continued Emission and a Brown Dwarf Companion
We report new observations of the unusually active, high proper motion L5e
dwarf 2MASS J13153094-2649513. Optical spectroscopy with Magellan/MagE reveals
persistent nonthermal emission, with narrow H I Balmer, Na I and K I lines all
observed in emission. Low-resolution near-infrared spectroscopy with IRTF/SpeX
indicates the presence of a low-temperature companion, which is resolved
through multi-epoch laser guide star adaptive optics imaging at Keck. The
comoving companion is separated by 338 \pm 4 mas, and its relative brightness
(\Delta K_s = 5.09 \pm 0.10) makes this system the second most extreme flux
ratio very low-mass binary identified to date. Resolved near-infrared
spectroscopy with Keck/OSIRIS identifies this companion as a T7 dwarf. The
absence of Li I absorption in combined-light optical spectroscopy constrains
the system age to >~0.8-1.0 Gyr, while the system's kinematics and unusually
low mass ratio (M_2/M_1 = 0.3-0.6) suggests that it is even older. A coevality
test of the components also indicates an older age, but reveals discrepancies
between evolutionary and atmosphere model fits of the secondary which are
likely attributable to poor reproduction of its near-infrared spectrum. With a
projected separation of 6.6 \pm 0.9 AU, the 2MASS J13153094-2649513 system is
too widely separated for mass exchange or magnetospheric interactions to be
powering its persistent nonthermal emission. Rather, the emission is probably
chromospheric in nature, signaling an inversion in the age-activity relation in
which strong magnetic fields are maintained by relatively old and massive
ultracool dwarfs.Comment: 15 pages, accepted for publication in Astrophysical Journa
Genetic Disruption of the Scaffolding Protein, Kinase Suppressor of Ras 1 (Ksr1), Differentially Regulates GM-CSF-Stimulated Hyperproliferation in Hematopoietic Progenitors Expressing Activating PTPN11 Mutants D61Y and E76K.
Role of Conserved Cysteines in the Alphavirus E3 Protein ▿
Alphavirus particles are covered by 80 glycoprotein spikes that are essential for viral entry. Spikes consist of the E2 receptor binding protein and the E1 fusion protein. Spike assembly occurs in the endoplasmic reticulum, where E1 associates with pE2, a precursor containing E3 and E2 proteins. E3 is a small, cysteine-rich, extracellular glycoprotein that mediates proper folding of pE2 and its subsequent association with E1. In addition, cleavage of E3 from the assembled spike is required to make the virus particles efficiently fusion competent. We have found that the E3 protein in Sindbis virus contains one disulfide bond between residues Cys19 and Cys25. Replacing either of these two critical cysteines resulted in mutants with attenuated titers. Replacing both cysteines with either alanine or serine resulted in double mutants that were lethal. Insertion of additional cysteines based on E3 proteins from other alphaviruses resulted in either sequential or nested disulfide bond patterns. E3 sequences that formed sequential disulfides yielded virus with near-wild-type titers, while those that contained nested disulfide bonds had attenuated activity. Our data indicate that the role of the cysteine residues in E3 is not primarily structural. We hypothesize that E3 has an enzymatic or functional role in virus assembly, and these possibilities are further discussed
Genetic disruption of the scaffolding protein, Kinase Suppressor of Ras 1 (KSR1), differentially regulates GM-CSF-stimulated hyperproliferation in hematopoietic progenitors expressing activating PTPN11 mutants D61Y and E76K
Activating PTPN11 mutants promote hematopoietic progenitor hyperactivation of Erk and hypersensitivity to GM-CSF. We hypothesized that Kinase Suppressor of Ras 1 (KSR1) contributes to activating PTPN11-induced GM-CSF hypersensitivity. Bone marrow progenitors from WT and KSR1−/− mice expressing WT Shp2, Shp2E76K, or Shp2D61Y were evaluated functionally and biochemically. KSR1 activation and interaction with phospho-Erk was enhanced in Shp2D61Y- and ShpE76K-expressing cells. Genetic disruption of KSR1 partially normalized Shp2E76K-induced GM-CSF hypersensitivity, but failed to correct Shp2D61Y-induced GM-CSF hypersensitivity. Collectively, these studies suggest that cells expressing Shp2E76K have a greater dependence on KSR1 for GM-CSF hypersensitivity than cells expressing Shp2D61Y